Reactivity of a (Bis-NHC)tricarbonylruthenium(0) Complex with Methyl Triflate and Methyl Iodide. Formation of Methyl- and Acetylruthenium(II) Derivatives: Experimental Results and Mechanistic DFT Calculations

Abstract

The ruthenium(0) complex [Ru{κ2 C 2-MeIm(CH2)3ImMe}(CO)3] (1), MeIm(CH2)3ImMe = 1,3-bis(3-methylimidazol-2-yliden-1-yl)propane, which contains a chelating bis(N-heterocyclic carbene) ligand, reacts with MeOTf at room temperature to give the ionic ruthenium(II) methyl derivative [RuMe{κ2 C 2-MeIm(CH2)3ImMe}(CO)3]OTf ([2]OTf), whereas an analogous reaction of 1 with MeI renders the neutral ruthenium(II) acetyl derivative [RuI{C(O)Me}{κ2 C 2-MeIm(CH2)3ImMe}(CO)2] (3), in which the iodide and acetyl ligands occupy mutually trans coordination sites. The fact that [2]OTf reacts with [Et4N]I to give 3 evidences the participation of the cationic species 2 + in the synthesis of 3. The mechanisms of these reactions in THF solution have been modeled by DFT calculations. They have shown that 2 + can be made from complex 1 and either MeOTf or MeI. In both cases, two plausible reaction pathways have been identified. They start with a rate-determining SN2 substitution process in which the metal atom of 1 attacks the C atom of MeI or MeOTf, displacing the corresponding anion to give, depending on how compound 1 approaches MeI or MeOTf, 2 + or a less stable isomeric species 2′+ that is easily transformed into 2 +. A subsequent CO migratory insertion in 2 + leads to an unsaturated (pentacoordinated) acetyl intermediate that easily adds the iodide anion to end in 3. DFT calculations have also shown that the reaction of 1 with MeOTf to give [2]OTf is thermodynamically more favorable than that of 1 with MeI to give [2]I due to the resonance stabilization and greater solvation energy of the triflate anion. These two effects are also responsible for the fact that the incorporation of the triflate anion with 2 + to give a putative triflate complex analogous to 3 is thermodynamically disfavored, whereas the incorporation of the iodide anion with 2 + to give 3 is thermodynamically favored.

Ru0 or RuII: A Study on Stabilizing the “Activated” Form of Ru-PNP Complexes with Additional Phosphine Ligands in Alcohol Dehydrogenation and Ester Hydrogenation

“…It is important to note that the alcohol oxidatively adds in a trans disposition to the Ru 0 center of 6 , forming a Ru II complex. − The same 0/2+ oxidation on ruthenium was observed by us with the Ru 0 complex 3 . When 8 and 9 are compared, complex 8 resembles a precursor to 9 , in which the transformation 8 → 9 is only precluded by the tight binding of PMe 3 to the ruthenium center.…”

Preparation and reactivity of a Ru(0) phosphino–carbene complex

“…4 Similarly, we have recently employed Ru(cod)(cot) 5 as a Ru(0) synthon for Rudithiolate-alkylidene complexes. 6 Other Ru(0) complexes are also accessible from the reactions of carbene donors with Ru 3 (CO) 12 , [7][8][9] while reduction of Ru(II) with reducing agents has also been used to access N 2 -adducts of Ru(0). 10 Similarly, pyrazolylphosphaalkene complexes of Ru(0) are known.…”

Homogeneous and Heterogeneous Chelation-Assisted Ruthenium(II)-Catalyzed C–H Functionalizations

“…A reasonable explanation for the crucial role of the acid would be an oxidative addition of acetic acid to ruthenium, but the addition of acetic acid without oxygen did not lead to any reaction (Scheme 62). Hence, an oxidative addition, like it is known for aryl [30] and alkyl halides [104] and also aryl ethers, [105] seems to be unlikely. The oxidation simultaneously requires oxygen and acetic acid.…”